Houdini 21.0 Nodes Dynamics nodes

Gas Dissipate 2.0 dynamics node

A microsolver that dissipates a field.

On this page
Since 21.0

Overview

The Gas Dissipate DOP is a microsolver used in building larger fluid simulations. The Fluid Solver and Smoke Solver DOPs allow microsolvers to be added before or after the main solver step to extend or tweak the simulation. Alternatively, advanced users may attempt to build an entire new solver out of microsolvers.

The Gas Dissipate DOP performs several types of dissipation on the specified field. This will drive the fields value to the goal value (usually zero), causing the smoke to disappear over time. An optional control field can be used to affect when the dissipation occurs. Using the heat field for a control will allow having dissipation be dependent on how long since the smoke was added to the simulation, if the solver is set to add the heat field.

Parameters

Time Scale

A scaling factor for time inside this solver. 1 is normal speed, greater than 1 speeds up the simulation, while less than 1 slows it down.

Dissipate

Enable Dissipation

Sets whenever to dissipate the field given by Source Field.

Dissipation

Mode

Controls the rate by which to dissipate the field.

Dissipation Rate

The percentage of the current amount lost per fixed interval (per second).

Subtraction Rate

Specific amount lost per fixed interval (per second).

Lifespan

The interval (per second) in which a fixed amount (1 unit) is lost.

Half-Life

The interval (per second) in which half the amount is lost (half-life).

Dissipation Rate

The percentage of the current amount lost per fixed interval (per second).

Subtraction Rate

Specific amount lost per fixed interval (per second).

Lifespan

The interval (per second) in which a fixed amount (1 unit) is lost.

Half Life

The interval (per second) in which half the amount is lost (half-life).

Goal Value

When turned on, controls the reference value to which the field will cool too.

Goal Tolerance

When this is turned on and the field’s value cools below Goal Value + Goal Tolerance, the field value will be driven down all the way to the Goal Value.

Dissipate Color

When this is turned on, the additional color field (given by Color Field) is also dissipated.

Goal Color

When Dissipate Color is turned on, this controls the reference color to which the color field (given by Color Field) will change too.

Use Control Field

When turned on, the dissipation is scaled by the control field.

Control Field

The name of the field to use to affect dissipation.

Control Range

Remaps (normalizes) the Control Field values based on the specified minimum and maximum. The output is used for scaling is always in a range of 0 to 1.

Remap Control Field

Allows the Control Ramp to change how the control field should scale dissipation between the minimum and maximum values of Control Range.

The following video shows the effect of having the Remap Control Field turned off, remap with an increasing control ramp, and remap with a decreasing control ramp.

Control Field Ramp

This ramp controls how the dissipation scale values are mapped between the minimum and maximum values of Control Range.

Use Bound Control

When turned on, the dissipation is scaled along one of the following directions.

Direction

Sets the direction along which to dissipate the field.

Bound Range

The minimum and maximum bounds along the set axis, in which the scale will remap to the range of 0 to 1.

Bound Control Ramp

This ramp controls how the dissipation scale values are mapped between the minimum and maximum values of Bound Range.

Diffusion

Enable Diffusion

Allows a fixed diffusion of the field in all directions. This is a time based blurring effect.

Radius

Controls the size of the diffusion in all directions. Larger values will make the field more blurred.

Filter

The shape of the blur kernel. In all cases, the box blur is the underlying method. If the blur is small or substepping large, one can likely get away with a box blur as it will become equivalent to a guassian blur with enough substeps.

Box

A simple box blur.

Cone

A cone shaped blur created by performing two box blurs.

Guassian

An approximation of a guassian blur by performing four box blurs.

Limit Volume

Minimum Limit

When turned on, limits the minimum value of the field.

Maximum Limit

When turned on, limits the maximum value of the field.

Bindings

Source Field

The name of the field to dissipate. This is a single scalar field.

Color Field

The name of the color field to dissipate when Dissipate Color is enabled.

Stencil Field

A scalar field to use as a stencil for where to perform this node’s computations. Voxels whose stencil value strictly exceeds 0.5 will have the operation applied, while the rest will be left unchanged.

Note

If a stencil field isn’t provided or does not exist, the operation will be performed everywhere.

Advanced

Use OpenCL

Use the OpenCL device to accelerate computations.

Inputs

All Inputs

Any microsolvers wired into these inputs will be executed prior to this node executing. The chain of nodes will thus be processed in a top-down manner.

Outputs

First Output

The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).

If no object stream is connected to this node, the output is a data output. This data output can be connected to an Apply Data DOP, or connected directly to a data input of another data node, to attach the data from this node to an object or another piece of data.

See also

Dynamics nodes